“What happens if they hold it for 4 years and Trump gets elected?”
It would be a different congress and not enforceable for one thing.
2 different congresses.
The house members serve for 2 year term and 1/3 of the senate is up for election every two years.
The clinton impeachment went over into a new congress. I couldn’t find where the House re-filed\re-voted the articles of impeachment in the 106th congress.
The house did have to reappoint impeachment managers but contended that: “In Congress impeachment proceedings are not discontinued by a recess;”
https://www.congress.gov/congressional-record/1999/01/06/house-section/article/H211-1